Switching elements, such as relays, piezoelectric actuators or solenoid valves—the latter, in particular, in the form of fuel injectors of an internal combustion engine—are subject to strict requirements during operation and are therefore frequently monitored. This monitoring may be carried out, for example, by evaluating voltages and/or currents of an actuator of the switching element, or with the aid of sensors which convert any physical variables into electrical variables. Additional lines are generally required to transmit these variables to a control unit or the like, which results in increased complexity.
In solenoid valves for direct gasoline injection of internal combustion engines, electrical control variables of the magnetic circuit may be used in many cases to ascertain the closing point in time of a nozzle needle of a fuel injector when the magnetic circuit directly activates the nozzle needle. Additional measuring lines or the like are frequently unnecessary. In contrast—for example for diesel injection—designs of fuel injectors exist in which the magnetic circuit first activates a servo valve, which subsequently controls a high pressure hydraulic system which activates the nozzle needle. The closing point in time of the nozzle needle is not ascertainable from the movement of a solenoid armature of the solenoid valve.